1. Field of the Invention
The invention relates to a method and a device for Internet Protocol (IP)-based transmission of information formed of a speech part and a data part in a communication system.
2. Description of the Related Art
As computers are integrated into communication services, IP-based transmission of information is also being increasingly used in communication systems. In addition to transmitting voice information for telephone services, information with both speech and data content is also being transmitted for several applications, such as video conferencing.
To ensure an optimum transmission speed or transmission bandwidth, the information is compressed before transmission. The speech part can be compressed with some loss. The algorithm used for this can however not be used for the data part of the information as this would lead to unwanted loss of information.
Furthermore, it is preferable to transmit the parts using different transport protocols. Accordingly, the information to be transmitted is divided into speech and data parts and transmitted separately.
FIG. 3 is a block diagram showing a device for transmitting information in a traditional communication system. The information from a sender 10 for a receiver 40 is first divided by an interface unit 20 into a speech part and a data part and then transmitted to a second interface unit 30. The separate transmission of the parts is controlled by a control message (arrow with dotted line). The arrow represents bi-directional data traffic as receipt is usually confirmed by a control message.
A traditional transmission operation in interface units 20 and 30 is shown in the left and right halves of FIG. 4. The first interface unit 20 receives information that comprises a speech part and data part from the sender 10 to be transmitted to the receiver 40. In the first stage (dividing), the information is divided into its component parts. In the second stage (coding), the speech and data parts are compressed and formatted according to the protocols used. The speech and data parts are transmitted to two different ports on the second interface unit 30.
So that the second interface unit 30 recognizes the identity of the parts, an appropriate control message is sent at a higher protocol level. In this example, a H.323 message is used to inform the second interface unit about the two ports. H.323 is a standard that defines components, procedures and protocols for audio-visual communication over packet-switched networks.
In a first stage (decoding), the second interface unit 30 interprets the received H.323 message and allocates the parts accordingly. In a second stage (combining), the original information formed from the parts is combined so that it can be forwarded to the receiver 40.
Since a connection has to be set up using the control message before transmission can occur, there is a time delay caused by transmitting, answering and processing the control message.